1. Field of the Invention
The invention relates to an internal combustion engine controller and in particular to a controller for a multi-cylinder internal combustion engine.
2. Description of the Related Art
In an internal combustion engine, fuel injected from a fuel injection valve into an intake port is partially vaporized and the remaining fuel attaches to the wall surface of the intake port. The fuel that attaches to the intake port wall surface is vaporized by the negative pressure in intake piping and the heat supplied from the intake port wall surface and forms a mixture together with the vaporized part of the fuel subsequently injected from the fuel injection valve. During steady operation, the amount of fuel that is injected from the fuel injection valve and attaches to the wall surface of the intake port and the amount of vaporization of the fuel that has attached to the wall surface of the intake port balance. Thus, it is possible to make the air-fuel ratio of the mixture formed in the cylinder the stoichiometric air-fuel ratio by injecting fuel, the amount of which corresponds to the stoichiometric air-fuel ratio, from the fuel injection valve.
However, when the internal combustion engine is started, especially when the engine is cold-started, the temperature in the intake piping and the temperature of the wall surface of the intake port are low and the negative pressure in the intake piping is not produced yet. In addition, the amount of fuel that has attached to the intake port since before the engine is started is not large. Thus, most of the fuel injected from the fuel injection valve at the time of starting the engine attaches to the wall surface of the intake port. For this reason, in order to form the mixture with an ignitable concentration in the cylinder, at least in the first cycle at the time of starting the engine, it is necessary to supply a larger amount of fuel than is supplied during steady operation after warm-up is completed. In addition, because fuel supply is performed for each cylinder, in the case of a multi-cylinder internal combustion engine with multiple cylinders, a large amount of fuel is supplied to the cylinders sequentially. However, when a large amount of fuel is supplied, a correspondingly large amount of unburned HC is discharged from the cylinders into the exhaust passage. Although the catalyst for purifying the exhaust gas is disposed in the exhaust passage, it takes a certain period of time for the purification ability of the catalyst to be activated during start-up when the temperature of the catalyst is low. Thus, it is desired to minimize the discharge of unburned HC from the cylinders at least until the catalyst is activated. Reduction of unburned HC produced at the time of start-up is regarded as one of the important issues related to the automobile having an internal combustion engine as the power source.
As solutions for the above issue, various technologies have been proposed. One of such proposals is a technology (hereinafter referred to as the related art) related to fuel supply at the time of starting a multi-cylinder internal combustion engine described in Japanese Patent Application Publication No. H08-338282 (JP-A-H08-338282). As described in JP-A-H08-338282, there is no need to supply a large amount of fuel into the cylinders consecutively in order to start a multi-cylinder internal combustion engine. It is possible to start an internal combustion engine even if fuel supply into part of the cylinders is stopped. When the engine is started with the fuel supply into part of the cylinders stopped, it is possible to significantly reduce the unburned HC discharged during start-up. The above related art is an invention made based on such knowledge. In this related art, the cylinder(s), to which fuel supply is performed, and the cylinder(s), to which fuel supply is stopped, are determined based on the result of identification of the cylinders during start-up and fuel supply into the cylinders is controlled according to the result of the determination. More specifically, in the above related art, the pattern of fuel supply into the cylinders is determined based on the water temperature at the time of start-up. A plurality of patterns of fuel supply that differ from each other depending on the water temperature, are prepared. In the patterns corresponding to high water temperatures, the number of cylinders, into which fuel supply is stopped, is set to a larger number and in the patterns corresponding to low water temperatures, the number of cylinders, into which fuel supply is stopped, is set to a smaller number. In all of these patterns, fuel supply into the cylinder, the timing of fuel supply into which comes first during start-up, is always performed. Moreover, regardless of which pattern is selected, the cycle, in which fuel supply is stopped, is the first cycle during start-up, and fuel supply is performed for all the cylinders in and after the second cycle if the start-up is completed.
In the above related art, into the cylinder(s), into which fuel supply is performed from the beginning of start-up, a large amount of fuel is supplied during the first fuel supply (the amount of fuel supplied during the first fuel supply is referred to as the start-up fuel supply amount, Qs). On the other hand, when the fuel supply into the cylinder(s), into which fuel supply has been stopped, is started, the amount of fuel supply into the cylinder(s) is not the start-up fuel supply amount Qs but the amount obtained by multiplying, by an increasing rate KK (>1.0), a post-start fuel supply amount, Qt, that is smaller than the start-up fuel supply amount Qs. As a result, the amount of the initial fuel supply into the cylinders, into which fuel supply is retarded (hereinafter referred to as the retarded start cylinder), is reduced as compared to that of the cylinder(s), into which fuel supply is performed from the beginning.
The amount of the initial fuel supply into the retarded start cylinder(s) can be reduced because of the following two operations caused by the retardation of the fuel supply. The first operation is the increase in the temperature in the cylinder(s) caused by the ineffective compression that occurs in the retarded start cylinder(s) and is accompanied by no combustion. The second operation is the occurrence of the negative pressure in the intake piping that accompanies the increase in the rotational speed of the internal combustion engine while fuel supply is retarded. Of these two operations, the latter, that is, the occurrence of the negative pressure in the intake piping particularly contributes to the reduction of the amount of fuel supply. When the intake piping negative pressure occurs, the atmosphere such that vaporization of the fuel is promoted in the retarded start cylinder(s) as compared to the cylinders, into which fuel supply is performed from the beginning, is created by the occurrence of the intake piping negative pressure. When vaporization of fuel is promoted, the amount of initial fuel supply into the retarded start cylinder(s) may be correspondingly reduced.
In the above related art, however, whether the start up has been completed is determined based on the rotational speed of the internal combustion engine and when it is determined that the start up has been completed in the first cycle during start up, fuel supply is sequentially performed into all the cylinders from the second cycle. However, the magnitude of the negative pressure produced in the intake piping depends not only on the rotational speed and therefore, a negative pressure enough to promote vaporization of fuel is not always produced in the intake piping when fuel supply into the retarded start cylinder(s) is started. It is considered that, in order to avoid misfiring caused by lack of fuel, it is difficult to significantly reduce the amount of initial fuel supply into the retarded start cylinder(s) as compared to the amount of initial fuel supply into the cylinder(s), into which fuel is supplied from the beginning.
As described above, in view of the reduction of unburned HC produced when the internal combustion engine is started, there is a room for improvement in the above related art.